Most people know that the Ford Model T was the first truly affordable automobile. But do you know what kind of engine it had? The original Model T, released in 1908, packed a 2.9-liter four-cylinder engine with just 22 horsepower.

That's a tiny output for its size compared to the engines of today, but it sure beat the engine in what's considered to be the first automobile -- the 1885 Benz Patent Motorwagen. That car had a single-piston engine and generated just two-thirds of a single horsepower.

As you can see, automobile engines have been in constant evolution since the very beginning of motoring. Today they are more powerful, quieter, more durable, less polluting and more fuel-efficient than they have ever been before, thanks to constant advancements in engine design and technology.

Automotive engineers are constantly working on ways to improve the internal combustion engine and carry it into the future. How many other inventions do you know that have been continuously refined for more 150 years?

In this article, we'll take a look at 10 of the biggest and most significant engine improvements of all time. From fuel injection to hybrid motors, we'll take a look at where engines have been, and hopefully get some insight on where they're headed.

10

The Four-stroke Engine Cycle

Historic car enthusiast Ian Sumner checks the engine of a Jaguar D-Type replica classic car which is displayed at the annual RNAS Yeovilton Air Day in Yeovil, England.

Remember that Benz Patent Motorwagen we talked about? In addition to having a single piston, or cylinder, it was a two-stroke engine, like many early motors. Stroke refers to the movement of the piston in the engine.

Four-stroke engines were one of the earliest improvements made to internal combustion engines in the late 1800s. On a four-stroke engine, there are four steps the engine takes as it burns gasoline: intake, compression, power, and exhaust [source: CompGoParts.com]. These steps all occur when as piston moves up and down two times.

Earlier, simpler two-stroke engines accomplish the same task -- burning gasoline to create mechanical motion -- but they do it in two steps. Today, two-stroke engines are found on small equipment like lawnmowers, small motorcycles, and large, industrial engines. Nearly all cars use the four-stroke cycle.

Four-stroke engines carry several benefits, including improved fuel economy, more durability, more power and torque, and cleaner emissions. However, compared to two-stroke engines, they are more complicated and expensive to make, and require the use of valves for the intake and exhaust of gases.

In spite of this, four-stroke engines have become the industry standard for cars, and they likely aren't going away any time soon. We'll learn more about the role of valves and how they've been improved upon later in this article.

Next, we'll learn about forced induction, and how it made its way from airplanes onto everyday cars.

9

Forced Induction

Turbochargers and superchargers are essentially air compressors that shove more air into the engine.

An engine requires three things to generate motion: fuel, air, and ignition. Cramming more air into an engine will increase the power generated by the engine's pistons. A long-standing way to do that, and one that's becoming increasingly popular as of late, is to use forced induction. You may know this process better by the parts that do make it happen -- turbochargers and superchargers.

In a forced induction engine, air is forced into the combustion chamber at a higher pressure than usual, creating a higher compression and more power from each stroke of the engine [source: Bowman]. Turbochargers and superchargers are essentially air compressors that shove more air into the engine.

Forced induction systems were used on aircraft engines long before they started being added to car engines in the 1920s. They are especially beneficial for small engines as they can generate a lot of extra power without increasing the engine's size or causing a dramatic drop in fuel economy.

A good example is the turbocharged Mini Cooper S, which only has a 1.6-liter engine but produces more than 200 horsepower in some applications. In addition, high-performance cars like the Porsche 911 Turbo or Corvette ZR-1 use forced induction to achieve tremendous gains in power.

The drawbacks? Cars that have turbochargers often require premium gasoline. Then there's the issue of turbo lag, where the power gains aren't felt until the turbocharger spools up at higher revolutions per minute (RPM). Engineers have helped reduce both of those drawbacks in recent years.

And with fuel economy and emissions standards getting stricter, many carmakers are turning to forced induction on smaller engines instead of building larger engines. On the newest Hyundai Sonata, for example, the top engine one can buy is no longer a V6, but a turbo four-cylinder.

Next up, we'll discuss why carburetors have practically become a thing of the past thanks to fuel injection.

For decades, the preferred method for mixing fuel and air and depositing it into the engine's combustion chamber was the carburetor. Press the accelerator pedal to full throttle, and the carburetor allows more air and fuel into the engine.

Since the late 1980s, carburetors have been almost completely replaced by fuel injection, a far more sophisticated and effective system of mixing fuel and air. Fuel injectors spray gasoline into the air intake manifold, where fuel and air mix together into a fine mist. That mix is brought into the combustion chamber by valves on each cylinder during the intake process. The engine's on-board computer controls the fuel injection process.

So why did fuel injection replace the carburetor? To put it simply, fuel injection just works better in every aspect. Computer-controlled fuel-injected engines are easier to start, especially on cold days, when carburetors could make things tricky. Engines with fuel injection are also more efficient and more responsive to changes in the throttle [source: Automedia].

They do have drawbacks in terms of their increased complexity. Fuel injection systems are more costly to repair than carburetors as well. However, they have become the industry standard for fuel delivery, and it doesn't look like carburetors will be making a comeback anytime soon.

In this next section, we'll discuss the next step in fuel injection technology known as direct injection.

Direct injection is a further refinement of the improvements made by fuel injection. As you may have guessed from its name, it allows fuel injection to "skip a step," which adds efficiency to the engine, and more power and improved fuel economy as a consequence.

On a direct injection engine, fuel is sprayed directly into the combustion chamber, not into the air intake manifold. Engine computers then make sure the fuel is burned exactly when and where it is needed, reducing waste. Direct injection provides a leaner mix of fuel, which burns more efficiently. In some ways it makes gasoline-powered engines more similar to diesel engines, which have always used a form of direct injection.

As we learned earlier, direct injection engines boast an increase in power and fuel economy over stand fuel injection systems. But they have their drawbacks as well. For one, the technology is a relatively new one, having come to market only in the last decade or so. More and more companies are starting to increase their use of direct injection, but it has yet to become the standard.

Sometimes, direct injection engines can exhibit the buildup of carbon deposits on the intake valves, which could cause reliability issues. Some car tuners have expressed difficulty with modifying direct injection engines as well. Despite these issues, direct injection is the hot new technology in the automotive world right now. Expect to see it on more and more cars as time goes on.

Over the past few years, cars have been trending towards being more lightweight in many ways. Automakers look for ways to reduce a vehicle's weight in order to generate better fuel economy and performance. One of the ways they've done that is largely by replacing engines made of iron with aluminum ones.

For many years, iron engine blocks were the industry standard. Today the majority of all new small engines use aluminum instead, though many large V8 engines still use iron blocks. Aluminum weighs far less than iron -- typically, an aluminum engine weighs half what an iron one weighs. That translates into an overall lighter weight for the car, which means better handling and more fuel efficiency [source: Murphy].

Aluminum does have some drawbacks, however. As a metal, it's not as strong as iron and doesn't hold up to high levels of heat as well. Many early aluminum block engines had problems with cylinders warping, leading to concerns over durability. Those problems have been largely solved, however, and aluminum has clearly asserted itself as the future of engines due to its weight-saving properties.

In this next section, we'll talk about how camshafts have revolutionized engine design.

5

Overhead Camshafts

The benefit to the overhead cam setup is that it allows for more intake and exhaust valves, meaning fuel, air and exhaust can move more freely through the engine, adding power.

You've probably heard the term "DOHC" or "dual overhead camshafts" when someone talks about an engine. Most people recognize it as a desirable feature to have, but what does it mean? The term refers to the number of overhead camshafts above each cylinder in the engine.

Camshafts are part of your car's valvetrain, which is a system that controls the flow of fuel and air into the cylinders. For many decades cars primarily had OHV engines, meaning overhead valves, also called "pushrods." Pushrods are driven by camshafts inside the engine block. This setup adds mass to the engine and can limit its overall speed.

On an overhead cam setup, the camshaft is much smaller and is inserted above the cylinder head itself, rather than in the engine block. There's one on a single overhead cam (SOHC) engine, while a DOHC engine has two. The benefit to the overhead cam setup is that it allows for more intake and exhaust valves, meaning fuel, air and exhaust can move more freely through the engine, adding power.

While many car companies have done away with pushrod engines, DOHC and SOHC haven't supplanted them quite yet. Chrysler still uses pushrods to generate lots of power for their Hemi V8 engines; General Motors utilizes pushrods on some of their high-tech, modern V8s as well. But DOHC and SOHC engines have been prominent on engines, especially smaller ones, since the 1980s.

The drawback of having overhead cams is that they increase complexity and cost. Are you noticing a trend here yet?

Next we'll learn more still about how valves affect performance when we talk about variable valve timing.

4

Variable Valve Timing

People who tune their Hondas for performance often speak of "VTEC kicking in." But what exactly does that mean?

If you're at all familiar with Honda engines, you've almost certainly heard the term VTEC. People who tune their Hondas for performance often speak of "VTEC kicking in." But what exactly does that mean?

VTEC refers to variable valve timing and lift electronic control, a form of variable valve timing. There are times when an engine requires more air flow, like during hard acceleration, but a traditional engine often does not allow enough air to flow, resulting in lower performance. Variable valve timing means the flow of air in and out of the valves is slowed down or sped up as needed [source: Autropolis].

Honda is hardly the only car company to offer such a system. Toyota has one they call VVT-i, for variable valve timing with intelligence, and BMW has a system called Valvetronic or VANOS, which stands for variable Nockenwellensteuerung, meaning variable camshaft control. While they all work a little differently, they all accomplish the same task -- allowing more air and fuel into the valves at different speeds. This makes an engine more flexible and allows it to deliver peak performance in a variety of conditions. It also increases fuel economy.

Many engines now incorporate some form of variable valve timing, often controlled by the engine's on-board computer. We'll talk about how engine computers have revolutionized design in this next section.

3

On-board Engine Computers

Modern cars have everything regulated by an on-board computer called an engine control unit, or ECU.

An engine is an incredibly sophisticated device. It has dozens of moving parts and has scores of different processes taking place at once. That's why modern cars have everything regulated by an on-board computer called an engine control unit, or ECU.

The ECU makes sure processes like ignition timing, the air/fuel mixture, fuel injection, idle speed, and others operate the way they're supposed to. It monitors what's going on in the engine using an array of sensors and performs millions of calculations each second in order to keep everything operating correctly. Other computers in the car control things like electrical systems, airbags, interior temperature, traction control, anti-lock brakes and the automatic transmission.

Cars have become increasingly computerized since the first on-board diagnostic (OBD) computers were added in the 1980s. That's the computer that's responsible for the "check engine" light on your dashboard. A mechanic can plug a computer into the OBD port and get a sense of your car's problem areas. They can't use OBD to immediately know what's wrong with your car, but it gives them a great starting point.

By making the engine run more efficiently, engine computers can result in greater fuel efficiency and easier diagnosis of problems. But they also make engines far more complicated, and can make them tricky for weekend mechanics to work on.

We've talked a lot about gasoline engines so far, but what about diesel engines? Diesels have never been big sellers in the United States. Despite their superior fuel economy over similar gas engines, many Americans still think of diesels as the noisy, sooty, smelly, unreliable motors of the 1970s and 1980s.

That's not the case anymore. The modern diesel engine is powerful, clean and extremely fuel-efficient. Today's engines use a low-sulfur form of diesel fuel, and systems within the car help eliminate particle matter and excess pollution.

The diesels made by companies like Volkswagen, Mercedes-Benz, BMW, Volvo and others boast engine improvements like turbocharging, sophisticated fuel injection, and computer control to provide a driving experience that's both efficient and high in torque [source: Bosch].

Diesel engines have some drawbacks, mainly their low RPM level and the higher cost of diesel fuel. But since many of them can achieve well over 40 miles per gallon (17 kilometers per liter) on the highway, the driver will need to pay for that fuel a lot less often. And if you're wondering if modern diesels offer good performance, look no further than the last few 24 Hours of Le Mans races, where Audi has dominated using a diesel racecar.

Finally, we'll look at the current leader in "green" cars -- the hybrid engine.

1

Hybrid Engines

One of the biggest engine improvements used to boost efficiency in recent years is the hybrid engine.

A combination of high gas prices, an increased awareness of the environment among drivers, and government regulations raising fuel economy and emissions standards have forced engines to "go green" more than ever before. One of the biggest engine improvements used to boost efficiency in recent years is the hybrid engine.

Hybrids were an obscure a decade ago, but now everyone knows how they work -- an electric motor is partnered with a traditional gasoline engine in order to achieve high fuel economy numbers, but without the "range anxiety" of an electric engine, where the driver always wonders what will happen when a charge runs out.

The Toyota Prius remains the top selling hybrid car in America. It boasts a 1.8-liter four cylinder engine coupled with an electric motor that produces 134 horsepower. At low speeds, the electric engine acts alone, meaning the car does not use gas at all. At other times, it assists the gasoline engine. The whole package gets about 50 miles per gallon (21.3 kilometers per liter) in both the city and the highway [source: AOL Autos].

Hybrids like the Prius represent the latest evolution in internal combustion technology. While their benefits come in the form of fuel efficiency, there are some drawbacks as well. Hybrids have a higher initial cost than their non-hybrid counterparts, and some have argued that gas must be much more expensive than it is now (unbelievable as that may sound) before the driver recoups the extra cost of the hybrid car.

However, it's clear that engines are trending towards reduced emissions and greater fuel-efficiency. While electric-only cars are becoming more common, it's clear the internal combustion engine isn't going anywhere quite yet. It will simply continue to evolve to be better and better, just like it has since the days of the Model T.